Semiconductor light emitting devices are increasingly been used in a wide variety of applications. In a particular example, luminaires using a number of light emitting diodes to emit light are increasingly being used for lighting applications to replace technologies such as incandescent light bulbs or fluorescent lamps. By mounting a plurality of light emitting diodes on a substrate, a variety of different light outputs can be achieved.
The light output of light emitting diodes in modern light emitting devices is typically limited by temperature related behaviour. One constraint on light output is provided by the thermo-electric behaviour of the semiconductor material of the light emitting diodes, for example thermal and current droop. In order to produce white light, a suitable phosphor is often used and the phosphor can quench at high temperatures. Therefore, the temperature of the phosphor needs to be kept below such temperatures with the light emitting diodes in use. However, typically phosphors are located adjacent to and in contact with light emitting diodes and hence as the light emitting diodes heat up the phosphor does too.
Light emitting devices are often required to work for long periods of time without replacement. In some cases, the light emitting devices are located at locations where access is difficult. Even where access is relatively straightforward, there is still a need for reasonable lifetimes. The long term reliability of light emitting diodes is often directly related to the temperature of the operating condition, with high temperatures leading to reduced lifetimes.
For all these reasons, the extraction of heat from light emitting device packages is necessary.
In conventional luminaires, light emitting diodes may be soldered to a substrate and heat generated in the light emitting diode passes by thermal conduction through the electrical contacts to the substrate. However, there is still a need for improved thermal management of light emitting diodes.